This invention relates to the treatment of largely contaminated aqueous effluents. In particular, it provides a two step method for removing virtually all of the metal ions from aqueous effluents prior to release to the environment.
The aqueous effluents of many industries contain metal ions. In the past, these wastes have been discharged to the environment with the attendant harmful effects. Recently, these harmful effects such as metal poisoning, have been recognized and strict limits on the metals discharged in aqueous effluents have been established by various regulatory agencies. It is known that many metal ions are stable in acid conditions and that when such acid solutions are neutralized, these metals will precipitate. However, such methods allow a significant amount of the metal ion to remain in solution, 10 ppm or more. A secondary treatment with perhaps an ion exchange resin is necessary to further reduce the metal ion in solution but these materials are expensive and require large amounts of water, chemicals and energy for regeneration.
In preparing this application, the arts dealing with waste water treatment and adsorption by magnesium silicate were reviewed and the most relevant reference appears to be our prior patent application Ser. No. 968,938, now U.S. Pat. No. 4,200,528. This application teaches that amorphous, hydrated magnesium silicate complexes metal ion, thereby effectively removing them from aqueous effluents. Large amounts of the silicate are required to achieve low levels of residual metal ion. About 5% silicate based on the weight of the effluent is required to reduce the metal ion concentration below about 1 ppm.
It is an object of this invention to exploit the synergism that occurs when treatment of an effluent with a base is followed by addition of a minimal amount of magnesium silicate to reduce the metal ion concentration to less than 0.1 ppm.